“People have to realize that if they are going to come, they are going to be subjected to the possibility of searches,” Evans said.
Police believe the expanded field and the “Boston Strong” solidarity that followed the attack could attract up to a million spectators — about twice the usual number. The Boston Athletic Association accepted 9,000 extra runners, including about 5,000 who were forced to stop last year and thousands more who want to run to pay tribute to the victims of the attack.
Security experts say the marathon presents a huge challenge.
“You need the convergence of luck and timing and fabulous intelligence, great police work. You need the stars and the moon and everything to line up together in order for it to be 100 percent safe,” said Robert Tucker, chief executive officer of T&M Protection Resources, a New York-based security firm.
Tucker said police would likely focus more resources on the finish line, where throngs of people gather, and ban any items that potentially add risk.
“They should forget about convenience and figure out what the real things are that they need to do to prevent something like what happened last year,” he said.
A list of new rules for runners includes a limit on the size of water bottles and restrictions on costumes — nothing bulky or covering the face.
Along the route, there will be more surveillance cameras and more police, including 400 armed military police from the National Guard, an unspecified number of undercover officers and hundreds more uniformed officers. Security will be especially tight at the start of the race in Hopkinton and at the finish line, where the largest crowds gather.
Police have gone out of state for special training on how to detect hidden explosives and to look for characteristics of someone who might be carrying a bomb.